Printing process and apparatus



Feb. 21, 1961 A, E, GEssLER ET AL 2,972,301

PRINTING PROCESS AND APPARATUS Filed April 6, 1954 mm R .f 4. mm

States Unite PRINTNG PROCESS AND APPARATUS Filed Apr. 6, 1954, Ser. No.421,242

8 Claims. (Cl. 101-426) This invention relates to printing, inparticular high speed printing of magazines and the like, and aims toprovide an improved method of printing at high speed with inks which setor dry rapidly. It also aims to provide new inks for use in thisprocess.

Until the early 1930s-typographic or lithographic inks used for printingwebs of paper were of two types. For printing of newsprint and similarabsorbent stocks, mineral oil inks were used; they dried by absorptionof vehicle into the paper. For super-calendered and coated papers whichwere less absorbent, inks made with oxidizing oil vehicles were used.Because of the slow drying ofthese inks, printing speeds were low and atraveling tympan was run with the paper to prevent offset and smearing.

The advent of heat drying printing inks (see Gessler U.S. Patent No.2,087,190) changed this picture radically, most particularly withrespect to web typographic printing on papers less absorbent thannews-stock (such as the super calendered and coated papers used formagazine printing). Prior to the instant invention, this has been donewith heat drying inks, much of it at speeds well over 1,000 feet perminute, and much of it multicolor work. Such inks are characteristicallybased on solutions of hard thermoplastic resins in petroleum derivedsolvents which, at usual ambient temperatures, have vapor pressuresbelow 0.05 mm. of mercury so that they evaporate very slowly on thepress, but leave the printed iilms fairly rapidly when the printed paperis passed through one of the heaters with which these presses areequipped and which bring the temperature of the web to about 300 F. to450 F. These solvent are characteristically parainic in nature, withboiling ranges between 450 and 600 F., and with vapor pressures of theorder of 0.05 to below 0.005 mm. at 95 F. corresponding to theproperties of normal paraffin hydrocarbons in the C14 to C15 range.

One diiiiculty with conventional high speed printing methods is that thehigh temperatures necessary to dry the ink are so close to the charpoint of the paper as to cause a reduction of the tensile strength ofthe paper. Where poorer grades of paper are used, or where the papervaries in quality from place to place in the web, this reduction ofstrength is sometimes suicient to cause the web to break, withconsequent loss of production time, and additional substantial paperwaste. Furthermore, the paper may become so brittle that trouble isencountered in folding, stapling and binding the signatures. Hence,reduction of heat has been a prime need of the industry.

Another disadvantage of heat drying inks has been that as press speedshave gone up, it has been necessary to approach their lower limit ofstability on the press by using solvents near the low end of range. As aresult, on shut downs, when the ink is not being replaced continuouslyby fresh ink feeding down from the fountain, solvent evaporates, and theink becomes tacky and unprintable. It has been necessary to spray therollers with solvent after shut downs, Vso the press can be startedVatent ICC without breaking the web due to excessive ink tack. Thisproduces large quantities of paper waste, since the mixture of solventand old ink must be removed by the paper until fresh ink works its waydown from the fountain. In web ofset printing, where plate scumming andstripping may occur when the ink is too thin, this necessity forspraying is a major hazard.

When heat drying inks were iirst introduced, press speeds of 500 feetper minute were conventional. As press builders stepped up press speeds,the necessary faster ink drying was accomplished partially by improvingthe ink drying ovens, and partially by changes in ink formulation. Theattainment of present day speeds of 1200 to 1500 feet per minute hasbrought ink formulation to the practical lower limit of ink stability onthe press so that mechanical progress in increasing press speeds hasbeen held up by the problem 'of ink stability.

Many attempts have been made to overcome the above diiculties, includingusing lower boiling solvents that would evaporate faster so that the inkcould be dried faster. Although such inks do dry faster, it has beenimpossible to use them heretofore because they evaporate too rapidly onthe distribution system of the press and cause prohibitive tacking up ofthe ink.

The expedient of enclosing Athe distribution system of the press hasbeen suggested by a number of workers, both to reduce solvent loss byevaporation and to prevent contamination of the atmosphere surroundingthe printing press by the evaporating solvent. It has been tried withboth resin-solvent based inks, and with water emulsion inks. While theenclosed system has been highly successful in gravure printing where theprinting roller revolves directly in the ink fountain, it has not provedsatisfactory for conventional typographic or lithographic printing.

In such printing, the ink is picked up from a fountain by a roller, andis transferred to other rollers, alternately metal and rubber, toproduce eventually on the plate an even lm a few ten thousandths of aninch in thickness. Generally, between ten and twenty rollers are used.In each transfer of ink, the thin ink film is literally torn in two,part remaining on the original roller, part transferring to the nextroller. The work done in splitting the iilm produces heattemperatures upto 140 F. have been observed on uncooled presses, and temperatures of to100 F. can be observed on some presses even where the metal rollers arewater cooled. During the splitting, the film is pulled into innumerablethin laments of less than l mil diameter, and in this form is exposed,ten to twenty times, to the atmosphere around the. distributing system,with a relative vmovement at press speeds equivalent to l5 to 20 milesper hour. Thisv extreme exposure of the lm has limited conventionaltypographic ink vehicles to very slowly evaporating solvents, even inclosed systems.

We have discovered that it is possible to print on presses havingextended distributing systems with solvent based inks which dry so muchmore rapidly than present day inks that even lsingle impressions cannotbe taken from an ordinary proof press. Our method permits the use ofsuper fast inks whose vehicles comprise resin solutions in organicsolvents with boiling ranges much below those of previous heat dryingink solvents, and, at ordinary ambient temperatures, whose vaporpressures and rates of evaporation may be l0 to 40 times that of thesolvents in previous heat drying inks. Our inks preferably employpetroleum derived solvents with boiling ranges -between 350 and 425 F.,corresponding to commercial parainic fractions whose principalconstituents can be ideally represented as n-hendecane and n-dodecane.

Our inks are not printable under ordinary ambient conditions ontypographie presses. According to our invention they are printable onsuch presses when the atmosphere surrounding the distributing system ofthe press contains a concentration of ink-solvent-vapor which ismaintained in such relationship to the temperature of the ink ilm on thedistributing system that the average ink film temperature does notexceed the dew point temperature of the solvent vapor of that atmosphereby more than a few degrees Fahrenheit, and preferably approximates thatdew point temperature. We have discovered that we can maintain thisrelationship by feeding into the vicinity of the press distributingsystem air or other gas, free of suspended droplets, and containing sucha concentration of solvent vapor that there is a tendency towardcondensation on the distributing system rather than evaporationfromtheink film. The distributing system is preferably enclosed, toconserve the atmosphere.

The atmosphere employed over the distributing system must be free ofsuspended droplets of solvent for two reasons. First of all, theexplosion hazard must be considered. According to the recognizedauthority, the U.S. Bureau of Mines (see Bulletin 503, pub. 1952, page68), the C to C12 hydrocarbons will not support combustion below 0.60 to0.67% in air. The normal C11 hydrocarbon (n-hendecane) yields aconcentration of 0.4% in air saturated with it at 120 F., 0.66% at 140F. While we worl; at temperatures of 105 F. and lower, there is thedanger that the concentration would increase to a point above theflammable limit if solvent droplets were permitted to be suspended inthe air. Hence, it is necessary, in the interest of safety, to remove byfiltration or baiing the suspended solvent droplets invariably presentwhen saturating a gas with solvent vapor.

These solvent droplets would present a second hazard-- if they woulddeposit on the ink, particularly on the form rollers or the plate, theywould not become suiiciently incorporated into the ink and would causeuneven printing.

While it is most desirable to keep condensation at a minimum on thepress in general, limited condensation on the traveling ink film is notobjectionable since the ultraiine initial condensate combines smoothlywith the ink nlm. Such condensation is minute in quantity and does notadversely influence the ink. However, condensation which producesdroplets of solvent would cause the sarne hazards as droplets entrainedin the air fed into the enclosure. Hence, we prefer to maintain thedistribution system at a temperature lower than those of the press frameand the enclosure, so that condensation will not occur except where itis immediately absorbed into the ink film before droplet formationoccurs by coalescence.

The process of our invention is useful with organic solvent inkswherever evaporation is a problem. For example, it will solve theproblem of drying on shut down occurring with the more volatile previousheat drying inks. But to get optimum benet from our invention, we preferto employ solvents with evaporation characteristics essentially similarto normal parain hydrocarbons of 1l to 12 carbon atoms. If slowerevaporating solvents are used, excessive heat must still be employed,while faster solvents introduce explosion hazards.

As indicated above, n-hendecane is a safe solvent, in the absence ofsuspended droplets. N-decane, however, crowds the explosive limits tooclose for safety-air saturated with n-decane at 100 F. contains 0.475%of decane, at 120 F. 0.855% and at 140 F. 1.58%.

The mixed parainic hydrocarbons commercialiy available in the C11-C12range contain, of course, some decanes, as well as some higherhydrocarbons. But they show practically no dernixing when gasitied underthe conditions of use. As aresult, we can use any para'tlinic cut in the350 to 425 F. boiling range, and get essentially the results obtainablewith n-hendecane and ndodecane.

While we prefer to use these petroleum distillates, our invention isapplicable to other organic solvents, bearing in mind the problems ofvolatility explosion hazard, and resistance of the press rollers to theaction of such solvents. For example, somewhat more volatile oxygenatedsolvents can be used, such as 2 ethyl hexyl acetate, since they havehigher flash points with respect to their volatility, provided they donot attack the rubber compositions used in the rollers of present dayhigh-speed presses.

Other solvents, such as naphthenic, aromatic and terpenic hydrocarbons,esters, ketones and the like, cannot be used on present day high-speedpresses, only because they attack the rubber compositions used on thedistributing rollers; they can be used with glue-glycerine compositionrollers, with which some slower presses are equipped, provided they havethe appropriate evaporation characteristics.

Our invention can be practiced Ywith advantage in all of those printingprocesses, such as typography or lithography, in which the inks are ofsuch character as to require distribution on an extended system ofdistributing rollers. It is useful in sheet fed presses, producingprints which will dry as they emerge from the press. But the greatestutility of the invention is in connection with high speed web printing,since it is in this field that it opens really new horizons. Theinvention can be used both for single and for multicolor printing.

To explain the invention more fully, reference should be had to thedrawing, which discloses schematically a four color press set up for thepractice of our invention.

The press comprises 4 separate units of substantially identical design,identified in the drawing by the color which is ordinarily printed bythe unit. Each unit consists of a printing cylinder 10 having a printingplate mounted on it, and an impression cylinder 11. A web 12 of paper isfed through the press by appropriate rollers.

Each plate is inked by a distributing system which comprises a series ofrollers operating between the fountain 13 and the plate. The metalfountain roller 14 takes ink from the fountain, and transfers it to arubber ductor roller 15, to a metal roller 16, to a rubber roller 17,thence to the oscillating metal ink storage roller 1S which can be watercooled. A rubber idler roller 19, takes the ink'to the final stages ofthe distributing system, contactlng both the cooled metal roller 20 andthe form roller 21 which inks the plate; roller 20 is in contact withdistributing roller 22 and form roller 2.4; the water ycooled metalroller 23 inks both the form rollers 24 and 25.

The entire press structure is surrounded by an enclosure 26, preferablyof some material such as glass, Lueite, or other transparent material;this enclosure is complete except for a slit 27 through which the webenters the enclosure, and a slit 2S through which the web leaves theenclosure. The enclosure is provided with appropriate hatches and doorsso that, for example, a pressman can get at any fountain from the top ofthe press, or so that the press can be entered from the side for thepurpose of changing plates and so on.

Means are provided for running air or other gas containing solvent vaporinto the press. This may comprise, for example, a saturator 47, in whichsolvent vapor is mixed with air or other gas. The solvent laden air,containing droplets, is passed through a bailie chamber 425 to removethe bulk of the droplets and then through a pair of mist eliminators 28Aof the centrifugal heme type. The solvent-vapor-containing air, free ofdroplets and mist, passes through a line 29 into the chamber throughports 30, so disposed as to distribute the solvent-vaporladen ait sothat dilution from fresh air, carried into the enclosure by web 12, willbe kept at a minimum. To dothis, the bulk. of the ports are preferablyplaced near the point .where Athe web .enters the enclosure, providingatv such point the greatest possible arnountv of saturated atmosphere. l

We have obtained,solvent-vapor-containing air by bubbling air through acolumn of solvent, and by evaporating solvent intoair; but a simpler wayto get solvent into the airs is by using as the saturator 47 a liquidsealed compressor consisting of a vanedrotor 3l, operating in a liquidseal 32 of solvent; To pass from the inlet ports 33 to the outlet ports34, any Vgasfed into the compressor must pass through the liquidsolvent, and thus it becomes substantially completely saturated withsolvent vapor` at the temperature andpressure in thepump chamber.

- We provide means for determining the dew point of the solvent in theenclosure. For example, a water cooled etched or ground mirror 36, witha temperature indicator 37, can be observed. As soon as its reectivityincreases on account of condensed vapor, the mirror loses its frostedappearance and the dew point temperature can then be read oii on thetemperature indicator. Most preferably, a photoelectric system forindicating the first increase in reflectivity (the dew point) is used incombination with a resistance thermometer or a sensitive thermocouple,attached to the surface of the mirror. All

readingsY can be made on instruments outside-the enclosure.

We also provide temperature measuring devices 40 at one or morestrategic points in the distributing system. These are connected, byelectrical leads 41, to registering devices outside of the pressenclosure where the ternperature can be read accurately. The registeringdevices are also, preferably, connected to controls which automaticallykeep the temperature of the rollers within a predetermined range. Asshown in the drawings, these devices 40 may be mounted on the largeoscillated water cooled roller 18, known in this particular distributingsystem as the ink storage roller.

VIn the'operation of the press, Vmake-ready is preferably done with slowdrying inks, with'thep'ress enclosurek open. When the plates areproperly adjusted and the make ready ink is removed the enclosure isclosed, and air containing solvent vapor is blown into the Ypress untilthe dew point indicator and the roller temperature indicators show'theproper relationship. This may be accomplished by maintaining atemperature in the saturatng compressor similar to that of the rollers.However, by cooling the rollers below the temperature of the vatmospherein the saturatingV compressor equilibrium can be obtained more rapidly,since complete saturation within the enclosure, at the highertemperature, is not necessary to establish the necessary dew pointtemperature-ink film temperature relationship. Printing is started whenequilibrium is indicated;

, During printing, solvent-vapor-saturated air is continuously fed intothe enclosure to replace atmosphere which leaks out or is carried out bythe moving web. A slight positive pressure is desirable in theenclosure. In the particular press enclosure shown, where the enclosurecontains about 120 cubic feet of air, we supplysolvent-vaporsaturated-airv from the compressor at the Vrate of onecubicfoot-per second, so that the atmospherein' the press is completelyreplaced about every two minutes. This constant sweep of atmospherethrough the press has the added advantage that neither occasional mist,nor the oftenV occurring minute droplets of ink which are thrown out vbythe` rollers rotating at high speed, can accumulate in the enclosurevtothe point where they will produce a hazard. Y

As printing progresses, the press temperatures rise. The work done insplitting the ink film to distribute it manifests itself as heat. AThiswork is proportional to the tackofV the ink. AIn four color printing,the first ink printed must necessarily be tackiest, and the other inksbecome progressivelymless tacky, VIr-Ience, the temperature lrisedue tothis effect is greatest on the yellow rollers in the`press shown, leaston the black.

solvent-vaporfAt `the same time, friction in the bearings produces heat,and causes the press frame to heat up. This effect may be less orgreater than the elect due to the work done in ink distribution. In thespecific experimental fourin-line press shown, frictional heat producedframe temperatures higher than roller temperatures on black and blueunits, but lower than roller temperatures on red and yellow units.

, As the temperature of vthe distributing systems rises, the dewpoint-press temperature relationship varies. Increase of the temperaturein the saturatng pump can maintain the relationship where only a singlecolor is being printed, or even where two color work is being done withinks of not too dissimilar body. But in four color process work, thetack relationship is such that each distribution system will operate ata difierenttemperature. For example, over a period of several hours inone experimental run with uncooled rollers, the black unit Went up to109 F., the blue to 112, the red to 113 and the yellow went to 119 F.Hence, it is necessary, inV order to maintain the desired relationship,either to provide a separate enclosure and saturatng unit for eachdistributing system, or, preferably, to cool the individual distributingsystems at different rates.

In actual practice, we prefer to regulate the temperature of both thesaturated atmosphere and the ink film in attaining our results.Maintenance of temperatures near or above body heat (98 F.) makes foruncomfortable working conditions. Similarly, cooling of the ink lilmeven down to 60 F. poses real problems to a cooling system.Additionally, ink loses tiow properties with decreasing temperatures,and flow can be obtained for low temperature work only by changes informulation which may hurt the lm properties. Hence, we stay in theWorking'range by both cooling the distribution system and raising thetemperature in the saturator, depending on the status of the system.With signals from the dew point indicator and the cooled rollers beingfed into avcontrol center, an operator can make his adjustments asindicated. The control center could be made automatic by connecting thenecessary servomechanisms to the indicators, and to the temperaturecontrols for the distributing system and the saturatng compressor.

Instead of the temperature indicating device on the distributing system,it is possible to mount a tack indicating device on the distributingsystem, and arrange for a signal to indicate when the'ink on the rollersbebegins to tack up-showing a change in equilibrium conditions. We lindthis type of device workable, but more cumbersome than the temperatureindicating device, and slower in providing the desired controls.

In determining the controlling temperatures, which are those of the inkfilms, it must be borne in mind that available devices for measuringunder dynamic conditions indicate roller temperatures, which are notidentical with ink lm temperatures. This difference is due to the heatdeveloped by the work done in tearing the ink apart in ydistributing it;the heat is removed from the ink by the refrigerant in the cooled metalrollers, which must be cooler than the ink film.

In our control mechanism, we measure the temperature of the outersurface of a water cooled roller, and comparative tests made with asurface pyrometer immediately after shutting down the press indicatethat the temperatures We measure While the press is in operation varyfrom the actual ink film temperatures. ink hlm on the black unit may befrom 2 to 5 F. warmer than the surface of the cooled steel rollers whilethe yellow unit may be from 10 to 15 F. higher, depending on time andspeed of run, and tacks of the ink. I

This greater tendency to heat up during printing, plus pick the paper,makes the first down yellow unit the sensitive one in the operation ofthe press.

For instance, the- In order that our invention will be completelyavailableto those skilled in the art, we will brieyrdescribe a speciiicexample of the practice of our new method.

The press was made ready, and the frame temperature determined to be 85F. The temperature of the solvent entering the saturating compressor wasmaintained at 94 F.; the solvent-Vapor containing atmosphere enteringthe enclosure, at six inches of water pressure, was 95 F. After tenminutes, the dew point temperature in the enclosure, as read at theyellow unit, was at 80 F. The inks of Example 1, infra, were placed intheir respective fountains; cooling water was started through therollers, and printing was started.

During printing, the surface temperature of the cooled rollers 18 waskept at 15 F. below the dew point temperature on the yellow unit, at 10F. below the dew point temperature on the red and blue units, and at F.below the dew point temperature on the black unit.

When printing started, the dew point temperature dropped a few degrees,due to the entrance of fresh air into the enclosure with the web. Thiscan be compensated for by increasing either the temperature or volurneof the solvent-vapor-saturated atmosphere being fed to the enclosure. Inthis instance, the rate of addition was such that the dew point waspermitted to rise a few degrees. For instance, in a 30 minute run at 800feet per minute, the dew point temperature first dropped from 80 F. to77 F., and then rose to 82 F. We were able to dry these inks at a webtemperature of only 200 F. and our printing results were excellent.

It is a feature of our invention that the balance which is maintainedduring printing can be preserved during the very diiierent conditionswhich obtain when the press is temporarily shut down. During printing,the identity of the ink on the distributing system is changingconstantly since it flows in a slow but steady stream over therollers-the atmosphere in the enclosure is being constantly diluted withfresh ink-the ink is being heated by the work done in distributingit-and the multitudinous thin lilaments of ink are being constantlyexposed to the atmosphere. During shut downs, the ink stands still-nofresh air is being drawn into the enclosure by the weband the ink isbeing cooled by the colder rollers, rather than being heated. Wecompensate for these dierences by stopping refrigeration of the rollers,and by reducing the amount of new solvent-vapor-saturated atmosphere fedinto the press.

When printing was interrupted in the course of the above-described run,the rate of feed of solvent-vaporcontaining atmosphere was reduced toone half of the rate of addition during printing, to prevent unduecondensation.

Despite these precautions, some condensation may occur on thewater-cooled rollers since residual cold water remains in them aftershut down. If the ink film has been maintained at approximately the dewpoint temperature during printing, this condensation is notobjectionable, and we prefer to operate accordingly.

Besides providing means for operating presses more rapidly, for reducingpaper Waste, and for producing signatures with more desirable mechanicalproperties, our process has two other marked advantages. First, theiinish obtainable with our inks is better than can be obtained bypresent day practice. This appears to be due to two reasons. One is thatthe inks with the lower boiling solvents can carry more of the glossproducing resin solids. The other is that far less penetration of thepaper occurs with these faster drying inks. This latter characteristicalso results in the use of substantially less ink.

The second marked advantage arises from economy in operating costs. Fuelbills for operating the drying units can be cut drastically, while thecost of saturating the air in the enclosure is a minor matter-thus, a.typical solvent will require only 1/3 pound to 1/2 pound of a very iThe foregoing description relates to atour color web,

press equipped with a single enclosure for all four printing units. Itwill be appreciated that this isA illustrative and thatl other types oftypographie or lithographie printing presses can be used in the practiceof our invention. Presses are so dissimilar in design that each type ofpress must be enclosed with an eye to a maximum economy and utility forthe particular press. In some types of web press, for example, it may besimpler and more economical to provide separate enclosures for eachdistributing system, rather than to enclose the whole press in a singlechamber. In other cases, it may be desirable to enclose the distributingsysternland most of the plate, but to leave the point of impressionoutside of the enclosure. This eliminates the problem of the web passingthrough the enclosure, but involves drying of the ink on the exposedplate during shut downs, which may be easily remedied by cleaning theplate before resumption of printing.

As indicated, while our invention can be practiced to advantage withconventional heat-drying inks at the'fast evaporating endy of the scale,the inks we prefer to use do not, so far as we are aware, have anyutility except in the practice of our process. These inks may bedescribed as dispersions of pigments in solutions of hard resins inappropriate organic solvents. Illustrative examples thereof are asfollows:

EXAMPLE 1.-SET OF PROCESS INKS A-Yellaw ink Benzidine yellow 15.50Pentalyn G (pentaerythritol ester of polymerized rosin) 46.10 Aluminumstearate 0.48 Oleic acid 2.86 Parafnic petroleum solvent-principallyhendecanes and dodecanes, boiling range 365 to 400 F., Kauri butanolvalue 32 35.06

100.00 B-Red ink Eosine red 17.00 Pentalyn G 47.18 Aluminum stearate0.66 Oleic Yacid 2.83 Parainic Petroleum solventprincipally hendecanesand dodecanes, boiling range 365 to 400 F., Kauri butanol value 32 32.33

100.00 C-Blue ink Peacock blue 22.40 Pentalyn G 39.71 Aluminum stearate...L 0.66 Oleic acid 2.86 Solvent as above 34.37

100.00 D--Black ink Carbon black 13.98 Furnace black 3.68 Clay 19.50Iron blue 3.03` Alkali blue in 0.56 Bodied linseed oil 0.77' Pentalyn G26.45 Soya lecithin 1.89 Oleic acid 2.83

Solvent as above 27.31

9 These inks had the following rheological properties (determined on arotational viscometer at 30 C.).

Viscosity (poises) Yield Value (dynes per sq. cm.)

100 r.p.m. 200 r.p.m. 100 r.p.m. 200 r.p.m.

Yellow 132 101 1, 41o 1, 920 R 69 62 135 390 41 a4 so 115 32 23 39o 540EXAMPLE 2 Single color black-Limed rosin type Carbon black 15.80 Furnaceblack 4.50 Clay 9.00 Talc 4.50 Wood rosin 29.65 Hydrated lime 1.91Gilsonte 2.81 Stearine pitch 1.56 Solvent of Example 1 30.27 100.00EXAMPLE 3 K Heavy-bodied single color black Carbon black 10.0 Furnaceblack 8.8 Clay 14.0 Methyl violet 0.1 Oleic acid 6% limed polypale(polymerized rosin) 30.3 Gilsonite 3.3 Solvent of Example 1` 33.2 100.0

Viscosity 161 poises at 77 F. and 30 r.p.m.

EXAMPLE 4 Single color black Carbon black 12.8 Furnace black 8.4 Clay9.0 Methyl violet 0.1 Oleic acid 0.3 Pentalyn G 34.0 Gilsonite 3.7

Paraflin petroleum solvent-boiling range 350 to This ink is at the fastend of our range. A similar binders may obviously be any lm former whichcan be used with the particular solvent employed, and which which theink contains' a volatile solvent which will cause the ink to dry up onthe distribution system under ordinary ambient conditions, whichcomprises maintaining a concentration of ink solvent vapor in theatmosphere over the ink distribution system in such relationship to thetemperature of the ink ilm on the distribution system that the inktemperautre does not exceed the solvent vapor dew point temperature bymore than a few degrees centigrade, by preparing at a point out ofContact with the distributing system a gas containing highconcentrations of ink solvent vapor, and continuously feeding said gastothe vicinity of the distribution system at such a rate asl to replacesuch gas as is removed from the vicinity of the distribution system bythe action of the moving web and other causes. r

2. The method of claim 1, in which the atmosphere about the distributionsystem is maintained by enclosing the distribution system, and theseparately prepared gas is continuously fed into the enclosure.

3. The method of claim 1, in which the separately prepared gas issubstantially free of suspended solvent droplets when fed into theenclosure.

4. The method of claim 1, in which the relationship is maintained byenclosing the distributing system, and by a combination of feeding intothe enclosure gas containing high concentrations of solvent vapor andfree of suspended solvent droplets, and by cooling the distributingsystem.

5. The method of claim 4, in which the distributing system comprisesrollers and a frame therefor, and the rollers are cooled below thetemperature of the frame.

6. The method of claim 1, in which the volatile organic solvent is analiphatic petroleum distillate in the 350 to 425 F. boiling range.

7. An apparatus for printing with an ink containing a solvent of suchvolatility that the ink is nnprintable from a press with an extendeddistribution system under gives a dry lm when the solvent evaporates. Itis necessary to use inks which will not swell the presently usedrollers-hence, aliphatic petroleum solvents are preferred. Butoxygenated solvents can also be used on most rollers; and pressesequipped with special rollers, or with glue glycerine rollers, can beused with napthenic, aromatic and terpene hydrocarbons.

We claim: 1. The method of printing on a moving web of paper by aprocess in which an ink is distributed over an extended distributionsystem to a printing plate and in ordinary ambient conditions,comprising a printing lpresswith an extended distribution system, anenclosure for the distribution system of the press,- means to mix gaswith solvent which produces a mixture substantially saturated withsolvent vapor and containing'suspended droplets, means to removesuspended solvent droplets from the mixture, means to feed said mixturewith suspended solvent droplets removed therefrom into the enclosure,and means to cool the distributing rollers of the press.

8. The apparatus of claim 7, having a dew point indicator in theenclosure, associated with means to determine temperature on thedistributing system, to permit of maintenance of the temperature of theink film in such relationship to the solvent vapor concentration in theenclosure that it never exceeds the solvent vapor dew point by more thana few degrees Fahrenheit.

- References Cited in the le of this patent UNITED STATES PATENTS1,805,144 `Tones May 12, 1931 1,837,702 Canfield Dec. 22, 1931 2,063,636Stevens etk al. .,Dec. 8,' 1936 2,063,672 Goddard Dec. 8, 1936 2,194,911Porter Mar. 26, 1940 2,272,406 Gurwick Feb. 10, 1942 2,282,158 Bennettet al. May 5, 1942 2,317,372 Gessler et al. Apr. 27, 1943 2,319,853Durham May 25, A1943 2,347,619 Taylor et al.` Apr. 25, 1944 2,409,215Lee Oct. 15, 1946 2,578,921 Cramer Dec. 18, 1951 2,614,493 Brodie Oct.21, 1952 2,649,381 Hempel et al. Aug. .18,1953 2,707,916 Smith et al.May 10, 1955

